Experimental Analysis of Venturi-Tube Behavior in Wet Gas Conditions

Subsea wet gas compressors have been successfully in operation for approximately 5 years. Their use has proven to
increase the recovery by approximately 10% and achieve a reliability up to 98%. Further developed and operation of subsea
wet gas compression requires detailed knowledge of compressor operability and how shift in operational conditions affect the
compressor system. The compressors ability to handle wet gas is documented in detail for a gas volume fraction limited down
to 0.90. The 4-5 last year of operation proves the wet gas concepts capability. As years pass by, well pressure and
production rate declines which causes the compressor operation point to shift towards the high head and low flow (surge) area of the characteristics. In addition, compressor inlet transients increase due to pipe surge (slugs), requiring a robust control system to prevent instabilities, e.g. compressor surge. It is therefore vital to understand how the compressor inlet flow
device behaves at different wet operation conditions. Accurate and reliable wet gas flow measurements are therefore crucial for establishing safe compressor operation.

Multiphase meters are used for wet gas flow metering to provide information about the total flow and liquid content. Most of these meters incorporate a venturi meter along with other sensors. Venturi tubes are the most considered the  suited single-phase meter for wet gas flow measurements. The reasons for this are their physical robustness to withstand erosion and the impact of liquid slugs at high velocities, their familiarity of use and the availability of standards for dry-gas conditions

The article documents how a standard dry gas venturi tube behave at different wet gas operation conditions. The venturi is
designed according to ISO5167-4 for dry gas conditions and is tested at the low-pressure air water compressor test rig at
NTNU. The objective of the current work is to document how wet gas affects the measurements and flow regime in a horizontally mounted venturi meter. Furthermore, it was of interest to connect the visible changes in flow regime to flow and pressure measurements and compare the wet gas overreading to previous work. To document overreading and flow regime
variation, a new transparent venturi tube was installed at the compressor inlet. The transparency of the venturi makes it
possible to visualize the flow mechanics though the venturi tube at different wet gas conditions. The venturi tube is tested in a GMF range from 1 to 0.83 at an air volume flow rate of 1.3m3/s.